BROWNSVILLE — On the dusty road into Sabal Palms Sanctuary, near the banks of the Rio Grande, a sign a mile from the entrance reassures visitors that despite the foreboding steel barricade ahead, no passport is required to enter through its gates.

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Confusion is understandable here. This once-thriving tourist destination was forced to close in 2009 amid uncertainty over the future of the 527-acre palm forest, one of just two tracts remaining, after the Department of Homeland Security raised a section of border fence north of it.

Since the sanctuary reopened in 2011, the towering rust-colored bars intended to slow the stream of illegal traffic from Mexico have done as much to ward off visitors, fearful of what is lurking on the other side.

“You hear lots of rumors,” said Jeanne Bork, an 80-year-old Midwesterner, who spends her winters in South Texas, and recently visited the sanctuary. “I heard somebody was murdered back here.”

Because of the snaking course of the Rio Grande, which marks the international boundary with Mexico, the border fence was built on top of the levee, in some places a mile or more from the river, marooning thousands of acres of bucolic farmland, native habitat sanctuaries and private landowners on its southern flank.

Today, there are roughly 56 miles of border fence and wall in the Rio Grande Valley alone, none of which changed the underlying character of the land — what was farmland before remains farmland today.

Yet, critics argue the fence not only disrupts communities and impedes residents' ability to move freely the nearer they are to the fence, it has also created a “constitution-free” region where Border Patrol enforcement faces less oversight.

“What they've essentially created is a no-go zone,” said Joseph Nevins, associate professor of geography and chairman of earth science and geography at Vassar College, who studies the U.S.-Mexico border and is familiar with the Rio Grande Valley. “The very act of being in a particular place invites suspicion.”

At least three times in recent years, witnesses reported that Border Patrol agents shot and killed people along the Texas-Mexico line without justification. One man in Matamoros was fatally shot from across the Rio Grande in Brownsville in July 2012.

On Friday, the Border Patrol directed its agents to limit their use of force in certain situations after a recent report by independent law enforcement experts criticized the Border Patrol for a policy that led to the killing of at least 19 people.

For its part, the agency says agents are authorized to search any vehicle between the fence and the river if they have “reasonable suspicion” unauthorized immigrants are aboard.

According to Mitra Ebadolahi, border litigation attorney for the American Civil Liberties Union, there is no legal principle that would suggest diminished constitutional protection when people are behind the fence.

“This idea that people are uniformly treated with suspicion just for being in a place that is technically U.S. soil is problematic from our point of view,” she said.

Standing sentinel

Before the fence went in the ground around Hidalgo, the high school cross-country team used to train on the levee that borders the town of nearly 12,000. Bird watching in the Lower Rio Grande National Wildlife Refuge on the south side of the fence was also popular during winter months.

To be near the fence now, much less pass through one of its gates, begs attention from Border Patrol, which invariably has a sentinel stationed near gaps in the fence. Familiar faces barely warrant a second glance, others are subject to identification checks and vehicle searches. Just outside the refuge entrance, there is a stack of makeshift ladders used to illegally scale the 18-foot-high steel barrier.

“If you're on the other side of the fence, you're either bird watching or up to no good,” said Martin Cepeda, Hidalgo's mayor. “But mostly people don't go out there, if you do, (the) Border Patrol is going to ask you your business.”

Over the past decade, the Border Patrol more than doubled its staff in Texas to roughly 9,700 agents, who employ high-tech gadgetry and tried-and-true techniques to counter human and drug trafficking. As a permanent structure, the fence serves to funnel traffic into gaps where the Border Patrol has the upper hand.

On a frigid January morning, infrared scanners detected movement nearby, and suddenly a voice crackled over the radio announcing that agents were in pursuit of three warm bodies, uncertain if they were foraging animals or stragglers from a group of 14 unauthorized immigrants arrested an hour earlier.

The agents dashed through a tangle of thorny brush, looking for sign of bent or broken tree limbs, discarded clothing and shoeprints. These fevered cat and mouse games south of the fence net thousands of arrests every month.

“I can tell you it's not a no man's land,” said Daniel Tirado, a Border Patrol spokesman in the Rio Grande Valley. “We are out there ... so are aliens and smugglers.”

For those whose livelihood is by the river, there is a heightened sense of being exposed to danger that few are willing discuss openly out of fear of retaliation from smugglers.

A couple of years ago, not long after the fence was built on the north side of Hidalgo County Water Improvement District No. 3, which pumps water directly from the Rio Grande to farmers and McAllen's public utility, employees working by the river were shot at from Mexico.

Othal E. Brand Jr., who chairs the water district, told his employees they had his blessing to carry concealed weapons to protect themselves. Brand even considered hiring security guards but struck a deal for increased Border Patrol presence instead.

“I do not like the turn-your-head attitude,” Brand said. “But that is exactly what you have to do if you are going to continue to work or live below the wall.”

On the 'Mexico' side

As one of the few citizens whose homes are south of the fence, Pamela Taylor has become dependent on the Border Patrol for her safety. Unlike some whose ancestors were awarded land grants by the Spanish king, precisely to encourage immigration, Taylor, 86, married into her two-acre plot in Brownsville. She met her husband during World War II and immigrated to South Texas in the late 1940s.

But the days of languid summer afternoons cooling off in the Rio Grande's twisting green waters, and migrant workers camped out in the front yard, bringing her fresh tortillas in the morning, are long gone. Her modest four-bedroom house still appears as an island surrounded by fields of cabbage in the winter and golden brown sorghum in the summer, but this pastoral vision belies the corridor for illegal traffic that unfolds nightly on her property.

These days, she is more likely to find a load of marijuana stashed in her front yard, or Border Patrol agents sipping on bottles of water from one of the coolers she keeps stocked on the dirt road in front of her house for thirsty passers-by. Strangers are warned the area is no longer safe.

“We're isolated ... stuck on the Mexican side,” she said. Far from providing security, Taylor said the fence has exposed her vulnerability. “The last thing I need is for people to know that I'm here alone.”

Nearly all of the Nature Conservancy's Lennox Foundation Southmost Preserve of native Tamaulipan thorn and endangered wildlife habitat lies behind the fence. Citing safety concerns, the site manager, who lived on the preserve, was moved after the fence was built, and without his on-site presence, the preserve is unable to host researchers there, a significant part of its mission.

For an 8.31-acre slice of land on the northern edge of the 1,034-acre preserve, the federal government paid almost

$1 million, but, according to Vanessa Martin, a spokeswoman for the Nature Conservancy, the money will not compensate for the long-term impact.

“Without knowing if we're going to have the same access to public safety, we're unable to steward the preserve as closely,” she said, “Naturally, visitation has declined.”

Further up the Valley, in the neighborhood of Ranchito, in Cameron County, children keep a safe distance from the fence, which casts an imposing shadow in their backyards. “I don't want them to take me to Mexico,” said 8-year-old Marco Yañez.

Yañez's father, Miguel, 40, pointed to his dented chain-link fence, the result of a Border Patrol chase through his backyard. After the fence was built, the pursuits stopped, said Yañez's brother-in-law, Javier Rodriguez Jr., 28.

Rodriguez worked on a crew that built the fence here, and he spoke glowingly of the $12-per-hour wage and weekly bonuses. As he spoke, a Border Patrol unit drove slowly along the levee, and a group of kids waved.

“The way I see it, it was just a way to put money on the table,” Rodriguez said.